Challenging a Newtonian prediction through Gaia wide binaries

TL;DR

This study tests Newtonian gravity using Gaia data on wide binaries and finds deviations at large separations, suggesting possible gravitational anomalies similar to dark matter effects at stellar scales.

Contribution

It provides the first empirical test of Newtonian predictions on wide binaries at large separations using Gaia data, challenging classical gravity models.

Findings

Consistent with Newtonian predictions below 7000 AU.

Inconsistent with Newtonian predictions at larger separations.

Indicates possible gravitational anomalies at low accelerations.

Abstract

Under Newtonian dynamics, the relative motion of the components of a binary star should follow a Keplerian scaling with separation. Once orientation effects and a distribution of ellipticities are accounted for, dynamical evolution can be modelled to include the effects of Galactic tides and stellar mass perturbers, over the lifetime of the solar neighbourhood. This furnishes a prediction for the relative velocity between the components of a binary and their projected separation. Taking a carefully selected small sample of 81 solar neighbourhood wide binaries from the {\it Hipparcos} catalogue, we identify these same stars in the recent Gaia DR2, to test the prediction mentioned using the latest and most accurate astrometry available. The results are consistent with the Newtonian prediction for projected separations below 7000 AU, but inconsistent with it at larger separations, where accelerations are expected to be lower than the critical $a_{0}=1.2 \times 10^{-10} $ { m s$^{-2}$} value of MONDian gravity. This result challenges Newtonian gravity at low accelerations and shows clearly the appearance of gravitational anomalies of the type usually attributed to dark matter at galactic scales, now at much smaller stellar scales.